1. Field of the Invention
The present invention relates to a method for manufacturing a thermoelectric semiconductor material or element and a method for manufacturing a thermoelectric module, and more particularly, it relates to a method for manufacturing a thermoelectric semiconductor material or element and a method for manufacturing a thermoelectric module effective in improving thermoelectric performance.
2. Description of the Related Art
Hitherto, thermoelectric elements that utilize thermoelectric phenomena have been employed as heat exchangers and temperature sensors. These thermoelectric phenomena are commonly known as the Peltier effect, Thomson effect and Seebeck effect, a description of each of which is given below.
The Peltier effect is a phenomenon arising when an electric current flows to the junction between different metal types and heat is generated or absorbed at the junction, and the Thomson effect is a phenomenon arising when an electric current flows to a metal which has a temperature gradient and heat is generated or absorbed at the junction. A Peltier element, which is used as an electro-cooler, is a thermoelectric element in which the above-described Peltier effect is utilized.
The Seebeck effect is a phenomenon in which, when the junction of metals of different type is maintained at a different temperature, an electromotive force is generated in the high temperature side and low temperature side of the sample, and thermoelements used as temperature sensors are thermoelectric elements which utilize this Seebeck effect.
Because the thermoelectric elements described above possess a simple structure, stable characteristics, and they are easy to handle, wide research and development is being undertaken with a view to their application in small-scale refrigerators as well as in the thermo-regulation of semiconductor lasers.
At the present time, alloys comprising 1 or 2 types chosen from a group comprising Tellurium (Te) and Selenium (Se), and 1 or 2 types chosen from a group comprising Bismuth (Bi) and Antimony (Sb), are used as the material for forming the above-described thermoelectric elements. These compounds, which are stratified-structure compounds, are semiconductors which, in the thermoelectrical characteristics attributable to crystal structures, possess anisotropic properties.
As a technique designed to improve the degree of orientation and the fineness of grains which comprise the stratified-structure compounds as described above, the quenching roller method is well known. The quenching roller method is a method for manufacturing thin films (hereinbelow referred to as "thin powders") with sub-micron class grains in which the stratified-structure compound, in a melted state, is caused to contact the surface of a rotating cooling roller. Examples of the prior art which disclose examples of the application of this quenching roller method include Japanese Patent Application Laid-open No. 8-306970 and Japanese Patent No. 2659309.
Japanese Patent Application Laid-open No 8-306970 discloses a technique in which the powder of thin powders obtained by the quenching roller method are solidified and molded using a hot press method. Because the powder of the thin powders obtained by the quenching roller method are configured from grains which have been made finer, based on the method described in Japanese Patent Application Laid-open No 8-306970, a thermoelectric element with high performance index can be expected.
Meanwhile, Japanese Patent No. 2659309 describes a technique in which thin powders, obtained by the quenching roller method, are laminated in the film thickness direction to effectively utilize the crystal orientation of the thin powders. In this quenching roller method, because the material which is in contact with the surface of the cooling roller is cooled from the center of the roller to the outer side, setting of the material occurs in the film thickness direction, and as a result, thin powders are obtained in which the C surface, which constitutes the base surface of the stratified-structure compound, is upright in the film thickness direction. If the thin powders are laminated in the film thickness direction, a thermoelectric element with high anisotropic properties is obtained.
In Japanese Patent No. 2659309, the thin powders laminated in the film thickness direction are pressed parallel to the film thickness direction to form the molded body, and terminals are attached thereto forming the thermoelectric element. An electric current is caused to flow from the terminals parallel to the film thickness direction of the thin powders wherein a thermoelectric element with high performance index, in which the anisotropic properties of the thin powders are utilized effectively, is produced.
However, in recent years, there has been a desire for thermoelectric elements with improved thermoelectric performance, and a search is underway for new techniques which further develop the above-noted techniques of the prior art.